In the fabrication process of a semiconductor device, shortening the waveform of a light to be used at a photolithography step is in progress for the high integration of the semiconductor device, and nowadays, a technology which uses an ArF excimer laser as a light source is about to be put to a practical use. A photolithography step using an ArF excimer laser, like a conventional photolithography step using g rays, i rays or the like, is executed by forming a resist film (hereinafter called “ArF resist film”) which is selectively exposed by the light of the ArF excimer laser, exposing the ArF resist film with a reticle on which a predetermined circuit pattern is formed, and then developing the film.
With the use of the ArF resist film patterned in this manner as a mask, various processes of forming trench interconnection elements, such as an etching process, a process of burying a metallic material by a CVD method, and an ion implantation process, are carried out. After execution of such processes, the ArF resist film which has become unnecessary should be removed. As a conventional method of removing the ArF resist film that becomes unneeded, for example, Unexamined Japanese Patent Application KOKAI Publication No. 2002-184741 discloses a method of altering a resist film to be water-soluble under atmosphere of water vapor and an ozone gas, and removing the resist film altered to be water-soluble by a rinse process.
The separation rate in the process for the ArF resist film using an ozone gas and water vapor is, however, extremely low. Therefore, it is difficult to employ that process in a production process which uses an ArF resist film. In general, an antireflection film (BARC) for preventing the reflection of an ArF excimer laser is formed as the base of the ArF resist film, but it is also difficult to remove the antireflection film by the process using ozone gas and water vapor. Further, not limited to the ArF resist film, as a resist film undergone an ion implantation process at a high dosage is hardened by implanted ions, it is also difficult to remove the resist film by only the process using ozone gas and water vapor.